Signal translating and modulating system



June 2, 1936. H. A. WHEELER` SIGNAL TRANSLATING' AND MODULATING SYSTEMFiled March 27, 1935 ATTORNEY.

www' v" UNITED STATES PATENT OFFICE SIGNAL TRANSLATING AND MODULATINGSYSTEM Harold A. Wheeler, Great Neck, N. Y., assigner to HazeltineCorporation, a corporation of Delaware Application March 27, 1935,Serial No. 13,227

21 Claims. (Cl. Z50-20) i My invention relates to signal-translating andIn the system described above, there is a certain -modulating systems,and more particularly to amount of unavoidable capacitive coupling be-:g such systems including a vacuum tube providedj tween each of theseveral electrodes upon which with a virtual cathode; that is, asecondary source,l is impressed a voltage and all of the other elecofelectrons controllable independently of thef trodes, this coupling beingeiective to transfer electron stream from the main cathode. g currentsfrom any given electrode to the circuits The invention is directedspecically to an arassociated with the other electrodes. Thesecurrangement for neutralizing, or compensating for, rents develop insuch circuits voltages which apany regenerative or degenerative feedbackeffect pear on their associated electrodes, and which l0 upon asignal-translating or -amplifying control are dependent upon theimpedances of the cir- 10 electrode of another electrode or electrodes,incuits at the frequency of the voltage impressed cluded in the samevacuum tube, and their conupon the given electrode. These inducedvoltages nected circuits, such other electrodes usually coon the otherelectrodes of the vacuum tube modioperating in the formation of thevirtual cathfy the effect of the given electrode upon the relo ode; andfor neutralizing or compensating for'any sultant electron currentflowing to the anode of 15 leInOdulating 0I' demOdulating eiect 0f theSignaithe vacuum tube and its associated output cirtranslating or-amplifying control electrode and cuit. The effect of these inducedvoltages may its connected circuit upon the modulating action be eitheraiding or opposing, depending upon in the same vacuum tube. whether thecircuits in which they appear are in- It has been proposed heretofore toutilize as a ductively or capacitively reactive at the fre- 20 modulatorof a signal-translating system, a multiqueney in question, electrodevacuum tube including means for form- The capacitive couplings betweenthe several ine a virtual cathode or secondary source of electrodes in emulti-electrode vacuum tube of electrons. Such a virtual cathode may beestabthe type described above, provided with a virtual lished by a pairof closely spaced electrodes, the cathode, is mede up of two components,the mst 25 one nearer the CathOde being maintained at a being the usualgeometrical capacitance, which DCSitiVe potential With respect theretOand the is dependent primarily upon the physical relationother at anEgatiVe pOtential With leSpeCt thel'eship of the electrodes within thevacuum tube. to. The latter electrode is effective to retard The secondComponent, which is peculiar to this the iiow of electrons beyond thefirst electrode type 0f vacuum tube including a, virtua1 cathode, 30 andto form a cloud or mass of slow-moving elecmay be termed a, space-Chargecoupung and is trcns having characteristics very similar to those due tovariations or fluctuations in the space of the actual cathode. Theintensity of the vir- Charge of the mass or Cloud of electrons consti..tual cathode may be @Ont/rolled by an emiSSiOn tuting the virtualcathode and positioned between control electrode interposed between thevirtual the vjrtua1cath0def0rming e1ectr0de5 It wm 35 and actualcathodeS. The eleCtiOn Stream from be understood that variations in thespace charge this virtual cathode may be C0nt1011ed by aSUitcapacitively induce displacement currents in the able electrodedisposed between the virtual cath- Circuits of any electrodes Subject tothe electro. V:ode and an output electrode further from they; static eldof the space Charge.

actual cathode. A signal-translating and -mOd- However, as betweencertain of the electrodes ulating system utilizing a Vacuum tube 0f met;of a multi-electrode vacuum tube, the capacitive i type J'llSt describedis disclosed and Claimed mii coupling is negligible, either because theyare re1- U' s' Letters Patent No' ,1958027 granted May atively remote orbecause of their electrostatic 4, 81934 upon my applica/mon' isolationby means of an interposed auxiliary 45 The aldantages of such a' Systemaie set forth screen electrode; for example, a screen adjacent mtietatnolr atthatnaggg 'lrllb the anode, which anode would otherwiseproduce tilii in an oscillator-modulator circuit, the the mst ntlceajbledlsturbmg eeci upon the signal amplification control or emission controlbias of the amplifying control electrode, or sigy ma be variedy as b anau electrodes because of the relatlvely high voltage nal Input electrodey y at which the anode operates. Further, the cirtomatic volume controlcircuit, without disturbing the characteristics of the oscillatorcircuit in- Cults aSSoClated with certain of the electrodes are cludingtwo electrodes nearer the actual cathode, usually tuned to widelydifferent frequencies so which generally constitute the grid and anodethat the impedances of certain of the circuits are of the oscillatorsection of the tube. low at the frequency of the voltage impressed upona given electrode, so that the voltage developed across such circuits isnegligible.

In particular, there exists an undesirable capacitive coupling,comprising mainly geometric capacitance such as described above, betweenthe signal input or amplification control electrode and the electrodewhich cooperates therewith to form a virtual cathode and which usuallyconstitutes also the anode of the oscillator section of the vacuum tube.This relatively high capacitive coupling is due particularly to therelatively close spacing of these two electrodes. This coupling resultsin two effects which may modify the overall conversion gain of thesystem.

In the first place, the trans-conductance between the signal inputelectrode and the adjacent electrode nearer the cathode, which mayconstitute the oscillator anode, produces a variation in the current inthe circuit of this latter electrode and develops upon the electrode avoltage of signal input frequency dependent in phase and magnitude uponthe impedance of this circuit. This voltage, in turn, capacitivelyinduces a current in the signal input circuit which develops upon thesignal input electrode a voltage dependent in phase and magnitude uponthe impedance of the signal input circuit and which may either aid oroppose the impressed signal input voltage. Since the trans-conductancebetween these electrodes is negative as compared with an ordinarytriode, an inductive impedance in the oscillator anode circuit withrespect to the signal frequency produces an effect which opposes that ofthe impressed signal input voltage; that is, eiectively reduces thisvoltage. This result is the usual one in systems in which the oscillatorfrequency is higher than the signal frequency and the oscillationcircuit is inductive at the signal frequency. This effect may be termed,broadly, regeneration and may be positive or negative (degeneration)dependent upon whether it increasesor decreases, respectively, thesignal input voltage. Although this regeneration does not directlyaffect the conversion gain of the tubeVits effect on the signal inputvoltage results in a change in the overall conversion gain of thesystem.

'Ihe capacitive coupling between the signal input electrode and theadjacent electrode nearer the cathode, that is, the oscillator anode,similar- 1y gives rise to a voltage of the oscillator frequency on thesignal input grid which may aid or oppose the action of the emissioncontrol electrode. This eifect may be termed, broadly, remodulation andmay be positive or negative (demodulation) dependent on whether it aidsor opposes, respectively, that of the emission control electrode. Thiseffect directly and correspondingly modies the conversion gain of thetube. Again, since the signal frequency is ordinarily below theoscillator frequency, the oscillator voltage on the adjacent electrodeis of opposite polarity to that on the emission control electrode, andthe signal input circuit is capacitive with respect to the oscillatorfrequency, this voltage on the signal input grid is of opposite polarityto that of the emission control electrode or oscillator grid, andtherefore produces a remodulating effect.

A third effect is due to what may be termed the space-charge couplingbetween the virtual cathode and the signal input electrode. Variationsin the space charge of the virtual cathode are produced primarily by theemission control electrode and, since a positive voltage on thiselectrode increases the negative space charge and thus the positivecharge induced upon the signal input grid, the space-charge coupling maybe considered as a negative capacitance between the two control grids.The nature of this coupling is thus opposite to that of the capacitivecoupling between the signal input electrode and the oscillator anodebut, due to the fact that the oscillator grid and anode voltages arealso opposite in phase, the resultant remodulating 10 effect of thespace-charge coupling is similar to,

and cumulative with, that of the geometric capacitive coupling describedabove, thus modifying the conversion gain of the tube in a similarmanner. 15

Thus it is seen that, under the particular conditions described, thatis, and oscillator-modulator in which the oscillator frequency is higherthan the signal input frequency, all three factors described abovecontribute to a reduction in the 20 overall conversion gain of thesystem.

It is an object of my invention, therefore, to provide asignal-translating and -modulating system, including a vacuum tube ofthe type described above, in which the behavior of the 2 modulator andassociated circuits is substantially independent of the capacitivecoupling of various kinds between the several electrodes thereof.

More specifically, it is an object of my invention to provide asignal-translating and -modu- :zo lating system, including a vacuum tubeof the type described above, in which an external interconnectionbetween the signal input electrode and the emission control electrodeeffects a transfer of current therebetween to compensate for, and toneutralize the effects of, the transfer of current between thesecircuits by the capacitive coupling therebetween, namely, thegeometrical and/or the space-charge coupling.

In accordance with my invention, a signaltranslating and -modulatingsystem including a vacuum tube having a cathode, a virtual cathode, anoutput electrode, and control electrodes for independently controllingthe electron current from the cathode and from the virtual cathode, isprovided with means for supplying currents to the signal input oramplification control electrode circuit and the emission controlelectrode circuit, the eifects of which are equal and opposite to thecapacitive coupling effects noted above. More specifically, inaccordance with my invention, the means for reducing the above-notedeffects of the capacitive coupling between the electrodes comprisesexternal capacitive couplings between the signal input or amplificationcontrol electrode and between the emission control electrode and pointsin the system the potential variations of which are related in a propermanner in phase and magnitude to those of the electrodes which give riseto the described disturbing eifects. For example, the coupling may bemade between the amplification control electrode and the emissioncontrol electrode adjacent the actual cathode, in case the tube isincluded in an oscillator-modulator system. In general, the value ofthis external coupling necessary to compensate for the geometricalcapacitive coupling, described above, may be determined from therelation that the ratio of the value of the external coupling to that ofthe inherent coupling between two electrodes is substantially equal tothe ratio of the amplitude of the potential variations of the electrodegiving rise to the disturbing effects to that of the point at which theexternal coupling is made. The value of the external coupling necessaryto comsinner eww ai '.'Jamaaasxf pensate for the space-charge couplingmay best be determined experimentally by adjusting the value of thiscoupling to neutralize the undesired capacitive couplings and thereby tosecure normal conversion gain.

For a better understanding of my invention, together with other andfurther objects thereof, reference is had to the following descriptiontaken in connection with the accompanying drawing, and its scope will bepointed out in the appended claims.

The single figure of the drawing is a schematic circuit diagram of acomplete superheterodyne radio receiver including anoscillator-modulator embodying my invention.

Referring now more particularly to the drawing, there is shownschematically a circuit diagram of a complete superheterodyne receivermodified in accordance with my invention. This receiver comprises aninput circuit I0 for connection between an antenna I I and ground,connected to a radio-frequency amplifier I2, the output circuit of whichis connected to a coupling transformer I3 tunable by a condenser I4. Thetunable circuit I 3-I 4 is connected to the signal input oramplification control electrode I5a of a vacuum tube I5 provided alsowith the usual cathode |5b of any suitable type and an anode |5c.Included in the circuit from cathode to ground is a biasing resistor I6and a by-pass condenser II.

The radio-frequency energy derived from the input circuit I0 may beutilized to modulate a source of local oscillations generated either ina separate tube or, as shown, in the tube I5 which i is provided withadditional electrodes I5d and I5c. The electrode I5e constitutes theemission control electrode or oscillator grid, while electrode I5dcomprises the oscillator anode and is connected to a suitable source ofdirect voltage, indicated as +B, through a resistor 22. The oscillationcircuit comprises a variable tuning condenser |9, and an aligningcondenser 2| connected in series across an inductance 20, this circuitbeing connected between the oscillator grid I5e and ground. A grid leaka is preferably connected from the junction of inductance 20 andcondenser 2| to the cathode |5b, as illustrated. A feedback from theoscillator anode circuit to the grid circuit is provided by means of aninductance 23 included in the anode circuit and coupled to theinductance 20; a condenser 24, directly coupling the lower terminals ofthe inductances 20 and 23; and the aligning condenser 2|, which iscommon to the oscillator grid and anode circuits. The vacuum tube I5 ispreferably provided also with a screen grid I5f interposed between theamplification control electrode I5a and the anode I5c and connected to asuitable source of direct voltage, indicated as -l-Screen, through aresistor 25 and a by-pass condenser 2B. The tuning condensers I4 and I 9are mechanically interlocked for unicontrol, as indicated by the dashlines interconnecting them, which unicontrol may be utilized also totune the circuits of the radio frequency amplifier I2.

The modulated carrier wave produced by the foregoing apparatus istransmitted through the tuned coupling transformer I8 to anintermediatefrequency amplifier 21, thence through a detector 28 and anaudio-frequency amplifier 29 to a sound reproducing device, such as aloudspeaker 30.

The above-described apparatus constitutes a conventional superheterodyneradio receiver, as modified in accordance with the teachings of myaforementioned patent, and, per se, constitutes no UUUI UII part of mypresent invention, so that a detailed explanation of its operation isdeemed unnecessary. In brief, the signal-modulated carrier wave receivedfrom the antenna circuit I0 is amplified in the radio-frequencyamplifier I 2 and, thus 5 amplified, is impressed upon the controlelectrode I5a of the combined oscillator-modulator I5. The cathode |517,oscillator grid I5e and anode I5d, together with their associatedcoupled oscillatory circuits, constitute a source of local oscillationswhich are effective to cause a periodic fluctuation in the emission fromthe cathode |5b and, thus, a periodic fluctuation in the availablesource of electrons for the amplification modulation section of the tubeI5.

As described in more detail in my aforementioned patent, the oscillatoranode I5d, which is of grid construction, is maintained at a positivepotential by virtue of its connection to the terminal +B and attractselectrons emitted from the cathode |5b which, because of their highvelocity, largely pass through the mesh of the electrode |5d. Themagnitude of this stream of electrons is caused to fiuctuateperiodically by virtue of the oscillator grid I 5e. The amplificationcontrol elec- 25 trode I5a, on the other hand, is maintained negativewith respect to the cathode I5b by the magnitude of the biasingpotential across resistor I6. This latter electrode is effective toretard the progress of the electrons beyond the oscillator 30 anode I5d,and a large portion of them is turned back toward the positively chargedelectrode I5d. This action results in a mass or cloud of electrons whichnormally exists between the electrodes I 5d and I5a., which has beentermed a virtual cath- 35 ode in that it has many of the characteristicsof the actual cathode, although it is not actually a cathode structure.

The electron emission from the secondary or virtual cathode iscontrolled by the electrode I 5a 40 in a manner very similar to thecontrol by a grid electrode in an ordinary triode. The result of thisarrangement is that the signal input voltage, impressed upon the controlelectrode I5a, is elective to modulate the locally produced oscillationsto produce an intermediate signal-modulated frequency which may beamplified and/or converted in any desired manner.

In a circuit arrangement of the type just described where, in general,the composite functions of emission and modulation or amplificationcontrol are effected in a single tube, there is a tendency toward amodification of the apparent conversion gain of the oscillator-modulatorsystem due to one or both of the effects of regeneration andremodulation. As stated above, these effects can be traced to theinherent coupling between the amplification or modulation controlelectrode and the emission control electrode and/0r the interposedelectrode, or their connected circuits. The term inherent coupling isemployed herein t0 denote the interelectrode capacitance between twoelectrodes, for example, the electrodes I5a and |5d, as Well as anyresidual capacitive coupling between their associated circuits.

In accordance with my invention, this effect on the conversion gain ofthe oscillator-modulator system is substantially eliminated orneutralized by an external coupling from the amplification controlelectrode I5a and the emission control 70 electrode I 5e to sources ofvoltage effective to transfer currents to their respective circuitshaving effects equal and opposite to those resulting from the inherentcapacitive coupling of these electrodes with one or more of theelectrodes with- 75 in the tube. This neutralizing effect may be derivedin any of a number of ways. For example, the amplification controlelectrode and the modulaton control electrode may be connected to pointsin the system at which the potential variations are related in phase andmagnitude to those which result in the above-described effects.

Specifically, when my invention is applied to an oscillator-modulator ofthe type described in which the potential variations of the oscillatorgrid l5e and anode |511 are in phase opposition, the amplificationcontrol electrode I5a and the oscillator grid l5e may be externallycapacitively coupled in any suitable manner, as by a condenser 3l. Bythis means not only is there developed on the signal input oramplification control electrode a voltage of oscillation frequencyeffective to compensate for that developed thereon by the inherentcapacitive coupling of this electrode with the oscillator anode 15d andby the space-charge coupling of the virtual cathode tending to effectremodulation, but also there is developed on the emission controlelectrode a voltage of signal input frequency effective to compensatefor that developed upon the oscillator anode ld and, by the inherentcapacitive coupling with the control electrode I5a, tending to effectregeneration. Thus, regeneration and remodulation are substantiallyeliminated and a maximum overall conversion gain of theoscillatormodulator system may be obtained.

As stated above, the value of the capacitance lof the coupling condenser3l required to neutralize that component of the capacitive couplingcomprising the geometrical capacitive coupling between the electrodes,is determined by the relation that the ratio of the capacitance of thecondenser 3l to that of the inherent coupling between the oscillatoranode I5d and the control electrode |5a is substantially equal to theratio of the amplitude of the potential variations of the electrode l5dto that of the oscillator grid l5e at which the external coupling ismade. The value of the external coupling necessary to compensate for theinherent space-charge coupling can be determined only experimentallyunder normal operating conditions, but it is generally of the order of afew micromicrofarads. The coupling condenser 24 may be adjusted to aidin neutralizing this latter coupling. In a specific circuit, utilizing apentagrid converter of the A1 type as the tube l5, a value ofcapacitance for the condenser 3l of from 1.0 to 1.3 micromicrofarads wasfound to be satisfactory.

While I have indicated sources of direct voltage symbolically denoted as-l-Screen and +B, it is to be understood that any suitable source ofoperating voltage for the system as a whole may be utilized, such as aconventional battery or a rectifier and filter.

While I have described what I at present consider the preferredembodiment of my invention, it will be obvious to those skilled in theart that various changes and modifications may be made therein withoutdeparting from my invention, and I, therefore, aim in the appendedclaims to cover all such changes and modifications as fall within thetrue spirit and scope of my invention.

What is claimed is:

1. A signal-translating and -modulating system including a vacuum tubehaving a cathode, an output electrode, and a plurality of gridelectrodes interposed therebetween, an input circuit connected to a rstof said grid electrodes, a circuit of substantial impedance connected toan adjacent grid electrode nearer said cathode, whereby a voltage ofinput frequency developed on said latter electrode has a regenerativeeffect on said input circuit, and means for substantially eliminatingthe effect of said regenerative action on the conversion gain of thesystem comprising means for supplying to one of said grid electrodes acurrent of input frequency having an effect on the resultant electronstream to said anode equal and opposite to that of said regenerativeeffect.

2. A signal-translating and -modulating systern including a vacuum tubehaving a cathode, at least three grid electrodes and an output electrodespaced in the order named, a signal input circuit connected to the thirdof said grid electrodes, a circuit of substantial impedance connected tothe second of said grid electrodes, whereby a voltage of input frequencydeveloped on said second electrode has a regenerative effect on saidinput circuit, and means for substantially eliminating the effect ofsaid regenerative action on the conversion gain of the system comprisingmeans for supplying to said first grid electrode a current of inputfrequency having an effect on the resultant electron stream equal andopposite to that of said regenerative effect.

` 3. A signal-translating and -modulating system including a vacuum tubehaving a cathode, an output electrode, and a plurality of gridelectrodes interposed therebetween, an input circuit connected to afirst of said grid electrodes, a circuit of substantial impedanceconnected to an adjacent grid electrode nearer said cathode, whereby I aVoltage of input frequency developed on said latter electrode has aregenerative effect on said input circuit, and means for substantiallyeliminating the effect of said regenerative action on the conversiongain of the system comprising an external capacitive coupling from oneof said grid electrodes to a point in said system the potentialvariations of which are related in phase and magnitude to thosedeveloped on scid second-named electrode.

4. A signal-translating and -modulating system including a vacuum tubehaving a cathode,an output electrode, and a pluralityof grid electrodesinterposed therebetween, a signal input circuit connected to a first ofsaid grid electrodes, a circuit including a source of oscillations andhaving a connection to at least one of the other of said gridelectrodes, an inherent capacitive coupling between said input electrodeand said other grid electrode, whereby a voltage of oscillationfrequency developed on said signal input electrode has a remcdulatingeffect on the output of said tube, and means for substantiallyeliminating the effect of said remodulating action on the conversiongain of the system comprising means for supplying to one of said gridelectrodes a current of oscillation frequency having an effect on theresultant electron stream to said anode equal and opposite to that ofsaid remodulating effect.

5. A signal-translating and -modulating system including a vacuum tubehaving a cathode, at least three grid electrodes and an output electrodespaced in the order named, a signal input circuit connected to the thirdof said grid electrodes, an oscillation system including connections tosaid first and second grid electrodes, an inherent capacitive couplingbetween said signal input electrode and said oscillation system and itsassociated electrodes, whereby a voltage of oscillation frequencydeveloped on said signal input @gime tNtHljY electrode has aremodulating eiect on the output of said tube, and means forsubstantially eliminating the effect of said remodulating action on theconversion gain of the system comprising means for supplying to one ofsaid grid electrodes a current of oscillation frequency having an effecton the resultant electron stream to said anode equal and opposite tothat of said remodulating effect.

6. A signal-translating and -modulating system including a vacuum tubehaving a cathode, an output electrode, and a plurality of gridelectrodes interposed therebetween, a signal input circuit connected toa rst of said grid electrodes, a circuit including a source ofoscillations and having a connection to at least one of the other ofsaid grid electrodes, an inherent capacitive coupling between said inputelectrode and said other grid electrode, whereby a voltage ofoscillation frequency developed on said signal input electrode has aremodulating effect on the output of said tube, and means forsubstantially eliminating the effect of said remodulating action on theconversion gain of the system comprising an external capacitive couplingfrom said signal input electrode to a point in said system the potentialvariations of which are related in phase and magnitude to thosedeveloped on said signal input electrode by said capacitive coupling.

7. A signal-translating and -modulating systern including a vacuum tubehaving a cathode, a rst control electrode, a second control electrodeand an output electrode spaced in the order named, said tube havingmeans including a third electrode interposed between said controlelectrodes for forming a virtual cathode therebetween, a signal inputcircuit connected to one of said control electrodes, an emission controlcircuit connected to the other control electrode, said controlelectrodes having an inherent spacecharge coupling therebetween, wherebya voltage of emission control frequency developed on said signal inputelectrode has a remodulating effect on the output of said tube, andmeans for substantially eliminating the eiect of said remodulatingaction on the conversion gain of the system comprising means forsupplying to one of said electrodes a current of emission controlfrequency having an effect on the resultant electron stream to saidanode equal and opposite to that of said remodulating eiect.

8. A signal-translating and -modulating systern including a vacuum tubehaving a cathode, a rst control electrode, a second control electrodeand an output electrode spaced in the order named, said tube havingmeans including a third electrode interposed between said controlelectrodes for forming a virtual cathode therebetween, a signal inputcircuit connected to one of said control electrodes, an emission controlcircuit connected to the other control electrode, said controlelectrodes having an inherent spacecharge coupling therebetween wherebya voltage of emission control frequency developed on said signal inputelectrode has a remodulating eiect on the output of said tube, and meansfor substantially eliminating the effect of said remodulating action onthe conversion gain of the system comprising an external capacitivecoupling from said signal input electrode to a point in said system thepotential variations of which are related in phase and magnitude tothose developed upon said signal input electrode by said space-chargecoupling.

9. A signal-translating and -modulating system including a vacuum tubehaving a cathode, a flrst control electrode, a second control electrodeand an output electrode spaced in the order named, said tube havingmeans including a third electrode interposed between said controlelectrodes for forming a virtual cathode therebetween, said controlelectrodes having an inherent space-charge coupling therebetween andbeing effective to control the electron stream from said cathode andsaid virtual cathode, respectively, and a condenser connected betweensaid control electrodes eiective to neutralize said space-chargecoupling.

10. A signal-translating and -modulating system including a vacuum tubehaving a cathode, a rst control electrode, a second control electrodeand an output electrode spaced in the order named, said tube havingmeans including a third electrode interposed between said controlelectrodes for forming a virtual cathode therebetween, a signal inputcircuit connected to one of said control electrodes, a circuit includinga source of oscillations having a connection to the other of saidcontrol electrodes, whereby the space-charge coupling between saidcontrol electrodes develops a voltage of oscillation frequency upon saidsignal input electrode having a remodulating effect on the output ofsaid tube, and means for substantially eliminating the effect of saidremodulating action on the conversion gain of the system comprisingmeans for supplying to said signal input electrode a current ofoscillation frequency having an effect on the resultant electron streamto said anode equal and opposite to that of said remodulating eect.

11. A signal-translating and -Inodulating system including a vacuum tubehaving a cathode, a rst control electrode, a second control electrodeand an output electrode spaced in the order named, said tube havingmeans including a third electrode interposed between said controlelectrodes for forming a virtual cathode therebetween, said controlelectrodes being effective to control the electron stream from saidcathode and said virtual cathode, respectively, an oscillation circuitincluding connections to one of said control electrodes and said thirdelectrode, and means for substantially eliminating the effect of thecapacitive coupling between the other of said control electrodes andsaid oscillalation circuit and its associated electrodes comprlsing aneutralizing condenser connected between said control electrodes.

l2. A signal-translating and -modulating system including a vacuum tubehaving a cathode, a rst control electrode, a second control electrodeand an output electrode spaced in the order named, said tube havingmeans including a third electrode interposed between said controlelectrodes for forming a virtual cathode therebetween, a signal inputcircuit connected to one of said control electrodes, an oscillationcircuit including connections to the other of said control electrodesand to said third electrode, an inherent` capacitive coupling betweensaid input electrode and said third electrode, whereby a voltage ofoscillation frequency developed on said signal input electrode has aremodulating effect on the output of said tube, said control electrodeshaving an inherent space-charge coupling therebetween, whereby anadditional voltage of oscillation frequency developed on said signalinput electrode has an additional remodulating effect, and means forsubstantially eleminating the effect of said remodulating actions on theconversion gain of the system comprising means for supplying to one ormore oi.' said electrodes a current of oscillation frequency having aneiect on the resultant electron stream to said anode equal and oppositeto that of said remodulating effects.

13. A signal-translating and modulating system including a vacuum tubehaving a cathode, an output electrode, and a plurality of gridelectrodes interposed therebetween, an input circuit connected to afirst of said grid electrodes, a circuit of substantial impedanceconnected to an adjacent grid electrode nearer said cathode, whereby avoltage of input frequency developed on said latter electrode has aregenerative effect on said input circuit, a circuit including a sourceof oscillations and having a connection to at least one of said gridelectrodes other than said input electrode, an inherent capacitivecoupling between said input electrode and said last-mentioned electrodewhereby a voltage of oscillation frequency developed on said signalinput electrode has a remodulating effect on the output of said tube,and means for substantially eliminating the eiect on the conversion gainof the system of said regenerative and remodulating actions comprisingmeans for supplying to one of said grid electrodes a current of inputfrequency having an effect on the resultant electron stream to saidanode equal and opposite to that of said regenerative effect and meansfor supplying to one of said grid electrodes a current of oscillationfrequency having an effect on said resultant electron stream equal andopposite to that of said remodulating eiect.

14. A signal-translating and -modulating system including a vacuum tubehaving a cathode, a rst control electrode, a second control electrodeand an outputelectrode spacedin the order named, said tube having meansincluding a third electrode interposed between said control electrodesfor forming a virtual cathode therebetween, a signal input circuitconnected to one of said control electrodes, an oscillation circuitincluding connections to the other of said control electrodes, a circuitof substantial impedance connected to said third electrode, an inherentcapacitive coupling between said input electrode and said thirdelectrode whereby a voltage of input frequency developed on said latterelectrode has a regenerative eiect on said input circuit and whereby avoltage of oscillation frequency developed on said signal inputelectrode has a remodulating effect on the output of said tube, saidcontrol electrodes having an inherent spacecharge coupling therebetweenwhereby an additional voltage of oscillation frequency developed on saidsignal input electrode has an additional remodulating eiiect, and meansfor substantially eliminating the effect of said regenerative andremodulating actions on the conversion gain of the system comprisingmeans for supplying to said signal input circuit a current ofoscillation frequency equal and opposite to the currents induced thereinby said couplings and for supplying a current of signal input frequencyto one of said electrodes having an eiect on the resultant electronstream to said anode equal and opposite to that of said regenerativeeffect.

15. A signal-translating and -modulating system including a vacuum tubehaving a cathode, a rst control electrode, a second control electrodeand an output electrode spaced in the order named, said tube havingmeans including a third electrode interposed between said control eleQ-trodes for forming a virtual cathode therebetween, a signal inputcircuit connected to one of said control electrodes, an oscillationcircuit including connections to the other of said control electrodes, acircuit of substantial impedance connected to said third electrode, aninherent capacitive coupling between said input electrode and said thirdelectrode whereby a voltage of input frequency developed on said latterelectrode has a regenerative effect on said input circuit and whereby avoltage of oscillation frequency developed on said signal inputelectrode has a remodulating effect on the output of said tube, saidcontrol electrodes having an inherent space-charge coupling therebetweenwhereby an additional voltage of oscillation frequency developed on saidsignal input electrode has an additional remodulating eiect, and meansfor substantially eliminating the effect of said regenerative andremodulating actions on the conversion gain of the system comprising anexternal capacitive coupling between said control electrodes.

16. A signal-translating and -modulating system including a vacuum tubehaving a cathode, a rst control electrode, a second control electrodeand an output electrode spaced in the order named, said tube havingmeans including a third electrode interposed between said controlelectrodes for forming a virtual cathode between said controlelectrodes, a signal input circuit connected to said second controlelectrode, an oscillation system including connections to said firstcontrol electrode and to said interposed electrode, and means forsubstantially eliminating the eiect on the conversion gain of the systemof the inherent coupling between said signal input electrode and saidoscillation system and associated electrodes comprising a couplingbetween said control electrodes.

17. A signal-translating and -modulating system including a vacuum tubehaving a cathode, a first control electrode, a second control electrodeand an output electrode spaced in the order named, said tube havingmeans including a. third electrode interposed between said controlelectrodes for forming a virtual cathode between said controlelectrodes, a signal input circuit connected to one of said controlelectrodes, an oscillation system including connections to said firstcontrol electrode and to said interposed electrode, said oscillationcircuit operating at a. frequency substantially higher than said signalinput circuit, and means for substantially eliminating negativeregeneration due to the inherent coupling between said signal inputelectrode and said oscillation system and associated electrodescomprising a coupling between said control electrodes.

18. A signal-translating and -modulating system including a vacuum tubehaving a cathode, a rst control electrode, an auxiliary electrode, asecond control electrode, a screen electrode, and an output electrodespaced in the order named, said auxiliary electrode and said controlelectrode remote from said cathode together forming a virtual cathode,a. signal input circuit connected to one of said control electrodes, anoscillation circuit including connections to the other of said controlelectrodes and to said auxiliary electrode, a circuit including a sourceof voltage for maintaining said screen electrode positive with respectto said cathode, and means for substantially eliminating the eiect onthe conversion gain of the system of the inherent coupling between saidsignal input electrode and said oscillation circuit and associatedelectrodes comprising an external capacitive coupling between saidcontrol electrodes.

19. A signal-translating and -modulating system including a vacuum tubehaving a cathode, a first control electrode, a second control electrodeand an output electrode spaced in the order named, said tube havingmeans including a third electrode interposed between said controlelectrodes for forming a virtual cathode between said controlelectrodes, a signal input circuit connected to one of said controlelectrodes, an oscillation system including coupled circuits oneconnected between said cathode and said first control electrode and theother between said cathode and said interposed electrode, and means forsubstantially eliminating the effect on the conversion gain of thesystem of the inherent coupling between said signal input electrode andsaid oscillation system and associated electrodes comprising acapacitive coupling between said control electrodes and a secondcapacitive coupling between the coupled circuits of said oscillatorysystem.

20. A superheterodyne radio receiver comprising means forseletingndiamplifying a signalmodulated carrier wave, anoscillator-modulator for converting said carrier Wave into one of lowerfrequency comprising a vacuum tube having a cathode, a rst controlelectrode, an auxiliary electrode, a second control electrode and anoutput electrode spaced in the order named, said auxiliary electrode andsaid second control electrode cooperating to form a virtual cathode, acircuit coupling the output section of said ampli- GEUCH H001 fyingmeans to a rst of said control electrodes, an oscillation circuitincluding connections to the other of said control electrodes and tosaid auxiliary electrode, means for substantially eliminating the effecton the conversion gain of the receiver of the inherent coupling betweensaid first control electrode and said oscillation circuit and associatedelectrodes comprising an external coupling between said controlelectrodes, means coupled to the output electrode of saidoscillatormodulator for amplifying the output modulation frequencythereof, means for detecting said amplified modulation frequency, and asignal-reproducing device coupled to said detecting means.

21. In a superheterodyne radio receiver, a fresaid firstcontrolAelectogndsaid,cathode, andr a capacitanceelementggonnutedmbetween said control electrodes and proportionedsubstantially to neutralize atY therpsilwlatin frequency thespace-charge couplingj/rompsaid rst,cnnt1;ol electrode to said secondcontrol electrode caused by said virtual cathode.

HAROLD A. WHEELER.

